This invention relates to an improved method and apparatus for inserting post-stressing tendons in concrete structures.
In the fabrication of concrete structures, for example bridges, nuclear pressure and containment structures, the structure is formed with ducts therein for the reception of metal tendons which are post-stressed after the concrete has hardened. Such tendons take the form of a plurality of wires, bars or strands, hereinafter conveniently referred to as "strands." Depending upon the size of the structure and the loads which it will have to bear will depend the number of ducts formed in the structure and the size of these ducts. The number of strands which lie in each duct may vary from 2 to 90 or more and the cross-sectional size of the ducts will depend upon the number of strands that it is to receive. The normal method of positioning the strands into the duct is to feed them in one by one but in structures in which the lengths of the ducts or their vertical height are considerable or in which the curvatures of the duct profiles are severe or these effects occur in combination, feeding by this method is impossible and an alternative method must be used. Normally, the whole tendon is pre-assembled elsewhere, bound into a coil, transported to the structure and loaded into an uncoiler from hich it is pulled by a winch into the duct. The use of this alternative method requires adjacent covered factory accommodation, and a number of expensive items of mechanical plant and therefore much increased cable threading costs.
It is the main object of the present invention to provide a method and apparatus for using the normal method of one-by-one threading for all cables regardless of the severity of the threading difficulty.